Senate Republican leader Mitch McConnell said on Monday he opposed U.S. President Barack Obama's plans to normalize relations with Cuba, and spoke of steps lawmakers might take to rein in the new policy.

Speaking by telephone from his home state of Kentucky, McConnell said he agreed with the Senate's most outspoken critics of Obama's new Cuba policy, Republican Senator Marco Rubio of Florida and Democratic Senator Robert Menendez of New Jersey, "that it was a mistake."

Obama's actions to forge relations and expand commercial ties with the Communist-led island after half a century of hostility has divided Republicans in Congress and could weigh on the 2016 campaign for president.

McConnell said there were some "pretty obvious" ways to keep the policy from being fully implemented. Only Congress has the power to remove some barriers to relations with Cuba since "a number of sanctions" were written into law, he said. He said any U.S. ambassador to Cuba would require Senate approval.

"Look at Vietnam," McConnell said. "We normalized relations with them and they are a Communist regime that still represses people. Sometimes engagement works, sometimes it doesn't."